On Mon, Sep 25, 2023 at 4:56 PM Alejandro Colomar <alx@xxxxxxxxxx> wrote: > > Hi Axel, > > On Tue, Sep 19, 2023 at 12:02:04PM -0700, Axel Rasmussen wrote: > > The old FIXME noted that the zeroing was done to differentiate the two > > EINVAL cases. It's possible something like this was true historically, > > but in current Linux we zero it in *both* EINVAL cases, so this is at > > least no longer true. > > > > After reading the code, I can't determine any clear reason why we zero > > it in some cases but not in others. So, some simple advice we can give > > userspace is: if an error occurs, treat the contents of the structure as > > unspecified. Just re-initialize it before retrying UFFDIO_API again. > > > > Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> > > I can't apply this patch due to conflicts (due to not having applied two > of the previous ones). Please resend all remaining patches in following > revisions of the patch set. > > The applied ones are here: > > <https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/log/?h=contrib> > > It's kind of like Linux's 'next' branch. Thanks for the review Alex! I'll fix up the issues noted and send the remaining few patches this week. :) > > Cheers, > Alex > > > --- > > man2/ioctl_userfaultfd.2 | 16 ++++++++-------- > > 1 file changed, 8 insertions(+), 8 deletions(-) > > > > diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2 > > index 1aa9654be..29dca1f6b 100644 > > --- a/man2/ioctl_userfaultfd.2 > > +++ b/man2/ioctl_userfaultfd.2 > > @@ -272,6 +272,14 @@ operation returns 0 on success. > > On error, \-1 is returned and > > .I errno > > is set to indicate the error. > > +If an error occurs, > > +the kernel may zero the provided > > +.I uffdio_api > > +structure. > > +The caller should treat its contents as unspecified, > > +and reinitialize it before re-attempting another > > +.B UFFDIO_API > > +call. > > Possible errors include: > > .TP > > .B EFAULT > > @@ -305,14 +313,6 @@ twice, > > the first time with no features set, > > is explicitly allowed > > as per the two-step feature detection handshake. > > -.\" FIXME In the above error case, the returned 'uffdio_api' structure is > > -.\" zeroed out. Why is this done? This should be explained in the manual page. > > -.\" > > -.\" Mike Rapoport: > > -.\" In my understanding the uffdio_api > > -.\" structure is zeroed to allow the caller > > -.\" to distinguish the reasons for -EINVAL. > > -.\" > > .SS UFFDIO_REGISTER > > (Since Linux 4.3.) > > Register a memory address range with the userfaultfd object. > > -- > > 2.42.0.459.ge4e396fd5e-goog > >
